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| author | Ming Lei <ming.lei@redhat.com> | 2018-07-02 12:35:59 +0300 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-07-09 18:07:53 +0300 |
| commit | b04f50ab8a74129b3041a2836c33c916be3c6667 (patch) | |
| tree | ccf5718c53c6afabf85f3c2597994938147f7ac9 | |
| parent | 3f0cedc7e9a0b32e79c79d2aac0c96d2b870ae55 (diff) | |
| download | linux-b04f50ab8a74129b3041a2836c33c916be3c6667.tar.xz | |
blk-mq: only attempt to merge bio if there is rq in sw queue
Only attempt to merge bio iff the ctx->rq_list isn't empty, because:
1) for high-performance SSD, most of times dispatch may succeed, then
there may be nothing left in ctx->rq_list, so don't try to merge over
sw queue if it is empty, then we can save one acquiring of ctx->lock
2) we can't expect good merge performance on per-cpu sw queue, and missing
one merge on sw queue won't be a big deal since tasks can be scheduled from
one CPU to another.
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Tested-by: Kashyap Desai <kashyap.desai@broadcom.com>
Reported-by: Kashyap Desai <kashyap.desai@broadcom.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | block/blk-mq-sched.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 4e027f6108ae..f3b4b5ceb4d1 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -326,7 +326,8 @@ bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio) return e->type->ops.mq.bio_merge(hctx, bio); } - if (hctx->flags & BLK_MQ_F_SHOULD_MERGE) { + if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) && + !list_empty_careful(&ctx->rq_list)) { /* default per sw-queue merge */ spin_lock(&ctx->lock); ret = blk_mq_attempt_merge(q, ctx, bio); |